The invention in this case relates to a new and novel electrolyte particularly adapted for use in electrolytic capacitors and to capacitors containing this electrolyte.
It is desirable that electrolytes employed for capacitors be as safe as possible. Additionally it is desirable that the electrolyte not contain an alkali metal as the alkali metal tends to be reduced during operation of the capacitor and during this reduction tends to cause pitting of aluminum cathodes. Further, the electrolyte should be free of halides as the presence of halides tends to deteriorate the capacitors.
Additionally, for those capacitors to be used under operating conditions of high temperatures for example at about 125.degree. C. it is desirable that the vapor pressure of the electrolyte be as low as possible at these temperatures. This is particularly desirable when the capacitors employed are tantalum capacitors as these capacitors are frequently operated for long periods of time at high temperatures.
Ross, U.S. Pat. No. 2,759,132, shows tantalum and aluminum electrolyte capacitors containing as an electrolyte a quaternary amine salt of an oxidizing anion such as one having a nitro, nitrosa or other oxidizing substituent. Other Examples of amines disclosed are the salts of tetraethanol ammonium and tri-isopropanol ammonium cations.
Examples of the anions are the picrates, nitrophenolates, nitrophenyl and the nitro-beta-naphtholate. These electrolytes suffer from the disadvantages of being relatively unsafe to those employed in the production process as the anion are toxic and potentially explosive.
Ross, U.S. Pat. No. 2,866,139, shows an electrolytic capacitor in which a tantalum anode is employed and in which the electrolyte contains a salt of an organic amine cation and an aromatic anion possessing a quinoid structure. Examples of the anion disclosed are alizarin, tetrahyroxyquinone and alizalin sapherole B. Among the cations disclosed are the quaternary amines such as the tetraethylammonium and other quaternary amines. While the electrolyte of this patent is useful at high temperatures as the vapor pressure is low at high temperatures, it is not free of halides particularly the chloride. Additionally, the anions employed are so expensive so as to prohibit the large scale use of these electrolytes.
Ross, U.S. Pat. No. 3,300,693, also shows electrolytes for use in an electrolytic capacitor comprising in a tantalum anode and an electrolyte containing a salt of phosphoric acid and a quaternary ammonium cation such as the tetraethylammonium cation. While these electrolytes are useful at high temperatures as they exhibit low vapor pressures at high temperatures they are not free of halides particularly chlorides.